1. Field of the Invention
The present invention relates to a method for fabricating group-III nitride-based compound semiconductor devices grown on a substrate consisting of, for example, silicon and, more particularly, to a method for growing epitaxial layers of group-III nitride-based compound semiconductors by means of metalorganic chemical vapor deposition (to be referred to as MOCVD hereinafter).
2. Description of the Related Art
To realize high-efficiency, high-brightness blue and ultraviolet light-emitting diodes and lasers, group-III nitride and related compound semiconductors have been researched and developed in recent years. As a method for growing group-III nitride and related compound semiconductors, MOCVD is currently widely used.
In a typical MOCVD process, group-III nitride is grown hetero-epitaxially on a sapphire substrate which is most frequently used at present. However, since sapphire is an insulating material and extremely rigid, it is not easy to fabricate a group-III nitride-based semiconductor device on a sapphire substrate. Silicon is one of the proposed substrate materials to overcome this shortcoming because of its high quality, large size, low cost, and the potential application to integrated opto-electronic devices. However, due to the large differences in lattice constant and thermal expansion coefficient between the group-III nitride and silicon, it is really difficult to grow high quality epitaxial layer of group-III nitride-based compound semiconductor on a silicon substrate. In order to solve this problem, many attempts have been made to grow group-III nitrides on silicon substrates in the past decade using various kinds of materials as the intermediate layer between group-III nitride and silicon substrate. These include AIN (U.S. Pat. Nos. 5,239,188 and 5,389,571, and Appl. Phys. Lett. Vol. 72, 1998, pp. 415-417, and 551-553), carbonized silicon (Appl. Phys. Lett. Vol. 69, 1996, pp. 2264-2266), nitridized GaAs (Appl. Phys. Lett. Vol. 69, 1996, pp. 3566-3568), oxidized AlAs (Appl. Phys. Lett. Vol. 71, 1997, pp. 3569-3571), and xcex3-Al2O3 (Appl. Phys. Lett. Vol. 72, 1998, pp. 109-111). In particular, by using AIN as the intermediate layer and the molecular beam epitaxy technology, ultraviolet and violet light-emitting diodes of group-III nitride grown on silicon substrate have been demonstrated recently (Appl. Phys. Lett. Vol. 72, 1999, pp. 415-417). However, the turn-on voltages as well as the brightness of these diodes do not approach the performance levels of corresponding devices grown on sapphire substrates by MOCVD. Therefore, the crystal growth method needs to be further improved in order to enhance the crystallinity of the group-III nitride-based compound semiconductors and to fabricate good quality opto-electronic devices.
The present invention has been made in consideration of the above situation and as one of its objectives, provides for a group-III nitride-based compound semiconductor-based device which emits and detects light with a wavelength covering from green to ultraviolet ranges, and is formed on a silicon substrate, having the above mentioned advantages, e.g. high crystal quality, large wafer size, low cost, well-established processing technology, and potential application to integrating optical devices with electronic devices on the same silicon chip.
It is another objective of the present invention to provide a crystal growth method for a group-III nitride-based compound semiconductor on a silicon substrate, yielding high quality p- or n-type conductor layers with excellent characteristics so as to allow formation of an excellent p-n junction for fabrication of a group-III nitride-based light-emitting device, laser diode, photodetector, field effect transistor, and other opto-electronic devices.
According to the present invention, there is provided a crystal growth method for group-III nitride and related compound semiconductors on silicon substrates, comprising of the following steps:
Thermal treating a silicon (001) or (111) substrate which is a single crystal or coated with a thin amorphous silicon film or any stress-relief film or a combination of them in a MOCVD reactor chamber under hydrogen ambient at a high temperature (preferably over 900xc2x0 C.) for at least 5 minutes;
MOCVD-growing an ultra-thin (preferably less than 500 nm) amorphous silicon film on a part of or the entire surface of the above mentioned silicon (001) or (111) substrate at a lower temperature (preferably between 400-710xc2x0 C.) using hydrogen-diluted silane as precursor;
MOCVD-growing at least one periodic or non-periodic multi-layered buffer on the top of the formed ultra-thin amorphous silicon film at a low temperature (preferably between 400-750xc2x0 C.). Within the multi-layered buffer, the layers alternate between two types of compound semiconductors different from each other in lattice constant, energy band gap, layer thickness, and composition;
MOCVD-growing a single layer or multiple layers of group-III nitride-based compound semiconductors over the composite intermediate layers consisting of an ultra-thin amorphous silicon film or any stress-relief film or a combination of them and a multi-layered buffer at a higher temperature (preferably in the range of 750-900xc2x0 C.); and
MOCVD-growing at least one layer or multiple layers of group-III nitride-based compound semiconductors on the top of all of the intermediate layers to form an opto-electronic or electronic device at a high temperature (preferably higher than 900xc2x0 C.).
According to the present invention, the group-III nitride-based compound semiconductor layers can be doped n- or p-type as it is MOCVD-grown over the obtained composite intermediate layers on a silicon substrate with excellent characteristics so as to form an excellent p-n junction for fabricating group-III nitride-based opto-electronic devices.
Additional objectives and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and advantages of the invention may be realized and obtained by means of the techniques and combinations thereof particularly pointed out in the appended claims.